DCC50212 - Topic 1

TOPIC 1

INTRODUCTION OF
HYDROLOGICAL

This topic covers the
hydrological cycle with
diagram & effect the land use
towards the hydrological
cycle.

TOPIC 1 –

Introduction of hydrology

Sub topic 1-
i. Explain the concept

of river basin and
catchment area
ii. Discuss hydrology
cycle with diagram
iii. Discuss the climate
change impact to the
hydrological cycle
iv. Calculate the water
balance

TOPIC 1 –

Hydrology cycle &
process

CATCHMENT AREA

• A portion of the earth’s surface that
collects runoff and concentrates it at
furthest downstream point, known as the
catchment outlet.

• Watershed – used for small catchment
• Basin – used for large catchment

TOPIC 1 –

Hydrology cycle &
process

RIVER BASIN

• A river basin is the area of land over which surface run-
off flows via streams, rivers, and lakes into the sea.

• A river basin sends all the water that falls within it to a
central river, and from there to the ocean.

• A river basin drains all of the land around a major river.
• Basins are divided into watersheds, or land areas that

surround a small, river or lake.

i) Concept of Hydrology TOPIC 1 –

Introduction of hydrology

• It’s processes, water balance,
precipitation types, estimation of
precipitation, and analysis of
precipitation data.

• Also methods of measurement of
stream flow, stage discharge relation,
unit hydrograph theory, Transposition
of Hydrograph, Synthesis of hydrograph
from basin characteristics, stream flow
routing, flood frequency analysis and
attenuation of flood flows.

• Emphasis is given towards the
calculation of rainfall data and urban
drainage concept in developing new
areas.

WHATS IS TOPIC 1 –
HYDROLOGY?
Introduction of hydrology
• It is a science of water.

i) Concept of Hydrology • It is the science that deals with the occurrence, circulation
and distribution of water of the earth and earth’s
atmosphere.

A good understanding of the hydrologic processes is
important for the assessment of the water resources, their
management and conservation on global and regional scales.

• The study of water on, under, and over the Earth’s surface,
and from its origins to all its destinations on the earth is
called hydrology.

• The scientific study of water, seeking to explain the water
balance equation in terms of time and space, and assessing
the impact of physical and chemical processes and their
role in ecosystems.

Uses of Engineering TOPIC 1 –
Hydrology
Introduction of hydrology
• Used in connection with design and A wonderful serenity has taken
operations of hydraulic structure

• Used in prediction of flood over a spillway,
at highway culvert or in urban storm
drainage

• Used to assess the reservoir capacity
required to assure adequate water for
irrigation or municipal water supply during
drought

• Hydrology is an indispensable tool in
planning and building hydraulic structures.

• Hydrology is used for city water supply
design which is based on catchments area,
amount of rainfall, dry period, storage
capacity, runoff evaporation and
transpiration.

Cont…Uses of Engineering Hydrology TOPIC 1 –

Introduction of hydrology

Design spillway water Design hydraulic structure

Manage reservoir - dam Manage flood Design open channel drainage

TOPIC 1 –

Introduction of hydrology

Branches in Hydrology

study of water on, under, and over the Earth’s surface

1234

Surface water Ground water Ice and snow Limnology
hydrology hydrology hydrology hydrology

Hydrological cycle TOPIC 1 –

• The hydrologic cycle is the continuous, unsteady Hydrology cycle &
circulation of water from the atmosphere to and process
under the land surface and back to the atmosphere by
various processes.

• It is dynamic in that the quantity and quality of water
at a particular location may vary greatly with time.

• Temporal variations may occur in the atmosphere, on
land surface, in surface waters, and in the
groundwater of an area.

• Within the hydrologic cycle, water may appear in all
three of its states; solid, liquid, and gas.

How the water cycle works TOPIC 1 –

Solar energy heats up Hydrology cycle &
the oceans water surface, lake, river etc. process

Water falls as rain, snow

b) c)
condensation percipitation

Water vapour condenses into clouds

a) evaporation Some of rain infiltrates in soil

Water evaporates and rises into the air

d) Water surface
Water returns to the sea

Surface runoff makes its way into rivers and streams.
Rivers flow back into the ocean due to the force of gravity.

The cycle starts all over again.

Component of TOPIC 1 –
Hydrology Cycle
Hydrology cycle &
1. Evaporation process
2. Condensation
3. Precipitation
4. Surface Runoff
5. Interception
6. Transpiration
7. Infiltration
8. Underground water

1 Evaporation Evaporation TOPIC 1 –

• Evaporation is the process by which Hydrology cycle &
water is converted from its liquid form to process
its vapor form and thus transferred from
land and water masses to the Evaporation
atmosphere.

• The rate of evaporation depends upon:
i. Wind speed: the higher the wind
speed, the more evaporation
ii. Temperature: the higher the
temperature, the more evaporation
iii. Humidity: the lower the humidity,
the more evaporation

Evaporation pan

Condensation Condensation TOPIC 1 –

Hydrology cycle &
process

2 Condensation

• Condensation is the process changes of
water from its gaseous form (water
vapor) into liquid water.

• Condensation generally occurs in the
atmosphere when warm air raises, cools
and looses its capacity to hold water
vapor.

• As a result, excess water vapor condenses
to form cloud droplets.

3 Precipitation Precipitation TOPIC 1 –

• Precipitation occurs when so much water has Hydrology cycle &
condensed that the air cannot hold it anymore. process

• The clouds get heavy and water falls back to the Precipitation
earth in the form of rain, hail, sleet or snow.

• Precipitation can occur primarily as rain. Annual
amounts of precipitation are unpredictable and
variable, ranging from approximately 1500 mm to
4000 mm in various locations in Malaysia.

• In essence, precipitation is the most important
process in the hydrologic cycle because it is the
'driving force' providing water that must be
accommodated in the urban environment.

Surface TOPIC 1 –
runoff
Hydrology cycle &
Surface process
runoff
4 Surface Runoff

• Sometimes referred to as overland flow, is the
process whereby water moves from the ground
surface to a waterway or water body.

• Surface runoff depend on type of surface,
saturated of topsoil, slope,& roughness of surface.

• Urbanization usually dramatically increase surface
runoff volume and rates.

TOPIC 1 –

Hydrology cycle &
process

Interception

5 Interception

• Interception is the amount of precipitation
that wets and adheres to above ground
objects (primarily vegetation) until it is
evaporated back into the atmosphere.

• The annual amount of interception in a
particular area is affected by factors such
as the amount and type of precipitation,
the extent and type of vegetation, and
winds.

• Interception is not likely to be an
important process in urban stormwater
management programs.

Transpiration TOPIC 1 –

Hydrology cycle &
process

6 Transpiration

• Transpiration is the process by which
moisture is carried through plants from
roots to small pores on the underside of
leaves, where it changes to vapor and is
released to the atmosphere.

• Transpiration is essentially evaporation of
water from plant leaves.

• Transpiration also includes a process
called guttation, which is the loss of water
in liquid form from the uninjured leaf or
stem of the plant, principally through
water stomata.

7 Infiltration TOPIC 1 –

Hydrology cycle &
• Infiltration is defined as the passage of water through the air- process
soil interface.

Infiltration • Infiltration rates are affected by factors such as time since
the rainfall event started, soil porosity and permeability,
antecedent soil moisture conditions, and presence of
vegetation.

• Infiltration is a very important process in urban stormwater
management and, therefore, essentially all hydrologic
methods explicitly account for infiltration.

• Urbanisation usually decreases infiltration with a resulting
increase in runoff volume and discharge.

https://www.youtube.com/watch?v=PYvfTxQhbOQ Double ring
infiltrometer

8 Underground water TOPIC 1 –

Hydrology cycle &
process

• Interflow, sometimes referred to as subsurface stormflow, is the
process whereby water moves laterally beneath the land surface, but
above the groundwater table.

• Interflow occurs until water enters a waterway or water body, or is
evapotranspired.

Subsurface • Interflow is affected by the same factors as those for surface runoff.
runoff

• Surface runoff, interflow, and precipitation falling directly on water
bodies are sometimes lumped together and called direct runoff.

Effect of land use toward TOPIC 1
hydrological cycle
–effect of land use

Natural Developed
Environment Environment

Rural area Urban area
– forest, recreation park, village residential, – city, school, residential area,
catchment area

The effect of soils use toward hydrological cycle TOPIC 1

–effect of land use

❑ When development occurs, the resultant alterations to the land can
lead to dramatics changes to the hydrology or the way water is
transported and stored,

❑ Impervious man-made surfaces (asphalt, concrete, rooftops) and
compacted earth associated with development create a barrier to
percolation of rainfall into the soil, increasing surface runoff and
decreasing groundwater infiltration.

Differential between TOPIC 1
type surface runoff
–effect of land use

Natural Ground Cover Low Density Residential TOPIC 1
0% Impervious Surface 10%-20% Impervious Surface
–effect of land use
Urban Residential Commercial Industrial
35%-50% Impervious Surface 75%-100% Impervious Surface Relationship
between

impervious
cover and

surface runoff

Impact of hydrological cycle. TOPIC 1

–effect of land use

This disruption of the natural water cycle leads to a number of changes, including:

i. Increased volume and velocity of runoff
ii. Increased frequency and severity of flooding
iii. Peak (storm) flows many times greater than in natural basins
iv. Loss of natural runoff storage capacity in vegetation, wetlands, and soil
v. Reduced groundwater recharge
vi. Decreased base flow (the groundwater contribution to streamflow). This can result in streams

becoming intermittent or dry, and also affects water temperature.

flood TOPIC 1

Land erosion Effects of land use to –effect of land use
the hydrological cycle
landslide

Global warming Water pollution

TOPIC 4

- Water balance

Hydrology Continuity Equation

Catshment & water budget

Where;

ΔS = change in storage, m3
Δt = duration of time, s
ΔZ = change in elevation, m
I = inflow, m3/s
O = outflow, m3/s
L = losses, m3
P = precipitation, m3
R = runoff, m3
A = area, m2

Inflow, I Outflow, O
Precipitation,P Runoff, R

Area, A ΔZ
Storage, m3

Hydrology continuity equation TOPIC 4

Inflow – Outflow = Change in Storage - Water balance

I–O = ds/dt Precipitation,P
Evaporation,E
I–O = ∆S
P – DRO – E – T- G = ∆S Transpiration, T
Direct runoff, DRO
Wher @ ∆S
e P – ( R + E + T + G) = Storage

G = Ground water Infiltration, I Ground water,
P = Precipitation G
R = Runoff or excess rainfall
DRO = direct runoff
B = Subsurface flow
I = Infiltration
ET = Evapotranspiration
E = Evaporation
T = Transpiration
S = Change in storage in the saturated

zone - soil or groundwater

Example 1 I1 = 10.0 m³/s I2 = 15.0 m³/s
O1 = 15.0 m³/s O2 = 16.0 m³/s
The storage in a river reach at a S1 = 20 x 10³ m³ Δt = 1 hour = 3600 s
particular time is 20 x 10³ m³. At a
particular time, the recorded I1 = 10.0 m³/sO1 = 15.0 m³/s I2 = 15.0 m³/s
inflow and outflow of the reach
are 10.0 m³/s and 15.0 m³/s O2 = 16.0 m³/s
respectively. An hour later the
inflow is 15.0 m³/s and the S1 = 20 x 10³ m³
outflow is 16.0 m³/s. Calculate the
change of storage and the new
storage volume of the reach at the
end of one hour.

The new storage, S2 = S1 + ΔS
= 20000 – 10800
= 9200 m³

Example 2 I=5 O = 5.5 1P3=5m6E0m=mm
m³/s m³/s
A lake had a water surface elevation of
100.0 m above datum at a beginning of a Area = 45 km2 Elevation = 100m
certain month. In that month, the lake
received an average inflow of 5.0 m³/s
from surface runoff sources. In the same
period, the outflow from the lake had an
average value of 5.5 m³/s. Further in that
month, the lake received a rainfall of 135
mm and the evaporation from the lake
surface was estimated to be 60 mm. The
average surface area of the lake was 45
km². Write the water budget equation
for the lake and calculate the new water
surface elevation of the lake at the end of
the month. Assume there is no
contribution to or from the groundwater
storage.

Example 3 Intensity rainfall = 100 mm/hr Volume runoff = 720000 m3
Area = 2.5 km2
Rainfall of intensity 100 mm/hr fell on a
catchment with area 2.5 km² for 6 hours. L =P–R L = Losses, m3
Measured runoff during this period was P = Precipitation, m3
recorded to be 720000 m³. Determine
the amount of water lost from this total 6 R = Runoff, m3
hours rainfall.

Thank’s

End of Topic 1 –
INTRODUCTION OF HYDROLOGY